This project is directed to exploration of the new concept that steroid hormone feedback can evoke not only changes in the amounts of LH and FSH released by the anterior pituitary, but also changes in the quality of the FSH and LH released by (and stored in) the anterior lobe. These qualitative changes may alter the capacity of the hormone to resist metabolic clearance processes and/or to bind to target cell receptors (or, having bound, to activate the cells). Information about when, and how rapidly, qualitative change occurs is being sought by manipulating gonadal steroid levels in the rat and examining pituitary and serum LH and FSH for qualitative change - using metabolic clearance patterns (seen by radioimmunoassay) and comparisons of activity ratios revealed by multiple assay methods (i.e. bioassay-immunoassay ratios). BIBLIOGRAPHIC REFERENCES: Bogdanove, E.M., J. M. Nolin and G. T. Campbell: Qualitative and Quantitative Gonad-Pituitary Feedback. Rec. Prog. Horm. Res. 31:567, 1975. Bogdanove, E.M., and A. M. Strash: Radioiodine escape is an unexpected source of radioimmunoassay error and chronic low level environmental contamination. Nature 257:426, 1975.